Problem: What number could replace $k$ below? $\dfrac{3}{4} = \dfrac{9}{k}$
The fraction on the left represents 3 out of 4 slices of a rectangular pizza. How many total slices would we need if we want the same amount of pizza in 9 slices? We would need to cut the pizza into 12 slices. $\dfrac{3}{4} = \dfrac{9}{12}$ and so the answer is $12$ Another way to get the answer is to multiply by $\dfrac{3}{3}$ $\dfrac{3}{3} = \dfrac{1}{1} = 1$ so really we are multiplying by 1. The final equation is: $\dfrac{3}{4} \times \dfrac{3}{3} = \dfrac{9}{12} $ so our answer is $12$.